Aquatic animals are commonly reared for commercial or research purposes and for the ornamental fish market, as well as (on occasion) for species preservation reasons. Current practices, whether in laboratory conditions or in commercial conditions, for rearing aquatic animals from embryo stages often manifest a mortality rate of more than 80%. Such a figure is typical in the case of zebrafish (Danio rerio) which are popular for use in genetic research and which, as a result, are often bred in laboratories. In genetic research particularly, such a high mortality rate can, result in the extinction of valuable species, strains or constructs, some of which may have an inherently diminished ability to survive. In commerce, this degree of mortality renders many forms of aquaculture marginally economically viable.
There is a growing need for commercial fish farming as many stocks of feral fish types have been fished almost to extinction.
Existing rearing practices leave a lot to be desired. For example, it is common to “catch” the animals being reared from time to time in a mesh sieve, as when transferring them from one container to another. Forced contact with hard surfaces results in perforation of the protective mucus layer of the animal which may result in infection of the animal by micro-organisms including pathogens.
It is undesirable that a growing animal wastes effort (and hence metabolites) in swimming against a current such as those resulting from recirculating equipment as used in the rearing environment.
Certain types of existing rearing containers include devices resembling chemist's separating funnels with a water flow introduced from below and overflowing at the top. There is a significant current, a risk of losses of animals by being caught in the overflow or injury caused by a restrictive screen.
Another rearing device makes use of a plastics box with a “V” shaped notched overflow at one end. Again, animals may be trapped in the overflow or lost from the container through the notch. Bubbles of air are frequently used for aerating and stirring the water but the resulting currents may be too severe for many purposes.
In this specification, the term “aquatic animal” is to be understood, unless the context clearly indicates otherwise, as a fresh water or marine water animal and includes vertebrate and invertebrate animals.